There is a need for research into bioindicators of stress in threatene
d plant communities such as coastal wetlands. Land subsidence, diversi
on of sediment, and salt water intrusion produce stresses associated w
ith waterlogging, elevated salinity, and nutrient depletion, Temporal
and spatial environmental variation (sell redox potential, interstitia
l water salinity, pH, ammonium and phosphorus, and cation and trace me
tal concentrations) was analyzed near Lake de Cade, Louisiana, in a br
ackish marsh which is a mosaic of healthy plant communities interspers
ed with areas where wetland loss is occurring. Environmental variation
was related to indicators of stress in Spartina patens, which include
d variables derived from the adenine nucleotide levels in plants, leaf
spectral reflectance, leaf proline concentrations, and shoot elongati
on. In a comparison of burned and unburned sites, streamside and inlan
d marsh, and along a salinity gradient, among-site differences were fo
und in spectral reflectance and adenine-nucleotide-related indicators.
Although it was difficult to relate a single causal environmental var
iable to the response of a specific indicator, spectral reflectance in
the visible light range responded to salinity or to elements borne in
seawater; and adenine-nucleotide indices were sensitive to nutrient a
vailability, The ability of indicators to detect plant responses chang
ed during the growing season, suggesting that they were responding to
the changing importance of different environmental factors, In additio
n, some reflectance indicator responses occurred along salinity gradie
nts when salinity differences were less than those that were found to
have ecologically meaningful effects in greenhouse experiments. A mult
ivariate numerical approach was used to relate environmental variation
with indicator responses. We concluded that factors which in combinat
ion cause the degradation and loss of Louisiana wetlands produce envir
onmental conditions that are only subtly different from those in vigor
ously growing marsh communities.